Off-road four wheeling, including hill and rock climbing, has long been popular with outdoor enthusiasts. In recent years, rock climbing, now commonly referred to as rock crawling, has grown exponentially in popularity. Rock crawling is a now a competitive sport utilizing a vehicle, a driver, and a spotter. The vehicle is typically classified in one of three competitive classes depending on the amount and type of modifications made to the vehicle to enhance its rock crawling ability. The rock crawling competition is a trials type of event, and scored much like a game of golf. The course on which the teams compete is laid out in a series of “obstacles”. The team with the lowest score is named the winner. The teams are scored with penalty and bonus points. General penalties include: stopping for more than four seconds, backing up, hitting the cones that are used to lay out the course, use of their winch, and using too much time. General bonus points are awarded for: not using a spotter's strap, progression gates, and hard bonus routes.
The rock crawling phenomenon has fueled a growing niche industry for aftermarket vendors of performance components for rock crawling vehicles including tires, suspensions, steering, drivetrains, etc. The most important of these performance improvements has been the development of options for achieving lower gear ratios, especially when considering that the growth of the sport has also resulted in the development of ever increasingly difficult trails and obstacles. Vehicles must typically have final crawl ratios ranging from about 100:1 to more than 200:1 to have a chance to negotiate some of the tougher obstacles.
The quest for low gear ratios has included lower ratios in each of the three components of the traditional drivetrain—the transmission, the transfer case, and the differential. The crawl ratio is determined by multiplying the highest gear reduction of these members. For example, a transmission having a first gear ratio of 4:1, a differential axle ratio of 5:1, and a transfer case with a low gear ratio of 4:1 results in a crawl ratio of 80:1. In seeking to increase the gear ratios, however, it has been found that the options for lower gear ratios at the transmission are limited by the available gearboxes themselves. Likewise, many differentials are limited by the available ring and pinion gear sets. Transfer cases utilizing chains or belts are typically not considered to be strong enough for rock climbing.
The transfer case provides the best option for achieving lower gear ratios. The general options available include: lower gear sets for existing transfer cases such as the Dana 300; new aftermarket transfer cases with low gear ratios such as the Atlas II from Advance Adapters; aftermarket gear reduction units mated to existing transfer cases such as the Klune-V; and double transfer case arrangements such as the Marlin Crawler. For shorter wheel base vehicles, the mating of aftermarket gear reduction units to existing transfer cases is impossible due to the lack of space available for the rear drive axle. The same problem exists for double transfer case arrangements.
One of the best performers has been the Atlas, and now the Atlas II transfer case, from Advanced Adapters. These units are known for their ruggedness and dependability and have a relatively small length. However, rock crawling competition creates some problems that are not particularly suited to the Atlas and other like transfer cases utilizing gears with shift fork slides. In rock crawling, it is often required to quickly engage or disengage the front and/or rear wheels. With gears and shift fork slides, the gears tend to bind, which prevents shifting. The driver often has to completely stop the vehicle or even go in reverse to shift the binded gears. As previously mentioned, stopping and reverse are penalized in rock climbing. It would, therefore, be an advantage to overcome one or more of the problems associated with the prior art transfer cases.